Observational evidence of dissipative photospheres in gamma-ray bursts

The emission from a gamma-ray burst (GRB) photosphere can give rise to a variety of spectral shapes. The spectrum can retain the shape of a Planck function or it can be broadened and have the shape of a Band function. This fact is best illustrated by studying GRB090902B: The main gamma-ray spectral component is initially close to a Planck function, which can only be explained by emission from the jet photosphere. Later, the same component evolves into a broader Band function. This burst thus provides observational evidence that the photosphere can give rise to a non-thermal spectrum. We show that such a broadening is most naturally explained by subphotospheric dissipation in the jet. The broadening mainly depends on the strength and location of the dissipation, on the magnetic field strength, and on the relation between the energy densities of thermal photons and of the electrons. We suggest that the evolution in spectral shape observed in GRB090902B is due to a decrease of the bulk Lorentz factor of the flow, leading to the main dissipation becoming subphotospheric. Such a change in the flow parameters can also explain the correlation observed between the peak energy of the spectrum and low-energy power law slope, alpha, a correlation commonly observed in GRBs. We conclude that photospheric emission could indeed be a ubiquitous feature during the prompt phase in GRBs and play a decisive role in creating the diverse spectral shapes and spectral evolutions that are observed.Comment: Submitted to MNRAS, 14 pages, 7 figure

La adquisición de vocabulario de una segunda lengua a través del análisis morfológico

El presente trabajo forma parte de un proyecto más amplio abocado al estudio del enriquecimiento del léxico inglés a través de la derivación morfológica. En esta investigación estudiamos los procesos que posibilitan la formación de sustantivos denominales, es decir, aquéllos cuya estructura incluye un sustantivo base. El corpus consta de 20 artículos periodísticos en inglés escritos en medios reconocidos durante el año 2013 y que versan sobre la temática ambiental. Seguimos los lineamientos teóricos propuestos por Biber et al. (1999) respecto a la derivación morfológica de sustantivos y adoptamos la terminología utilizada en el Manual de la Nueva Gramática de la Lengua Española (2009), ya que resulta de gran utilidad para traducir los conceptos descriptos en inglés. Para realizar el análisis, se clasificaron las palabras a partir de los afijos que las componen. Luego, se detectaron los afijos más utilizados y se especuló sobre el valor semántico de los mismos. Los resultados muestran que determinados afijos son más productivos ya que pueden colaborar en la construcción de nuevos sustantivos. El análisis morfológico ayuda al estudiante de una lengua extranjera tanto a comprender el significado de dichos vocablos, como también a producir nuevos sustantivos anexando afijos a palabras ya conocidas. En este contexto, el presente trabajo puede contribuir a perfeccionar las estrategias utilizadas en los procesos de enseñanza y de aprendizaje de vocabulario.This investigation is part of a larger project that aims to study the enrichment of the English lexicon by means of morphological derivation. In the present investigation, we analyze the processes that allow the formation of derivational denominal nouns, i.e., those whose internal structure includes a base noun and a derivational suffix. Our corpus is made up of 20 news articles about ecology written in English and published in prestigious online newspapers in 2013. We have followed the lines proposed by Biber et al. (1999) regarding the morphological structure of nouns and we have adopted the terminology used in Manual de la Nueva Gramática de la Lengua Española (2009), as we have found it very useful to translate the concepts described in English. In order to carry out the analysis, the selected words were classified according to the affixes they contained. Then, the most frequent affixes were identified and we made some speculations as regards the semantic value of them. Our results show that there are a number of affixes which are more productive as they more frequently help in the formation of new nouns. A morphological analysis helps a foreign language student not only to understand the meaning of those words, but also to produce new words adding suffixes to nouns they already know. In this context, this study may contribute to improving strategies in the processes of teaching and learning new vocabulary.Fil: Luque Colombres, María Candelaria. Facultad de Lenguas, Universidad Nacional de Córdoba Córdoba, Argentina.Fil: Batellino Valenti, Noelia. Facultad de Lenguas, Universidad Nacional de Córdoba Córdoba, Argentina